The present invention relates to a device for controlling transport claws in sewing machines, particularly in a sewing machine with cylindrical base, of the type comprising vertical motion-imparting means operatively connected with a first control shaft to transmit a reciprocating oscillatory motion in an essentially vertical direction and at least one transport claw operatively housed in the base of the sewing machine, horizontal motion-imparting means operatively connected with a second control shaft to transmit to said claw a reciprocating motion in a horizontal direction.
The subject device is especially conceived for use on sewing machine of the type with cylindrical base, whereto particular reference shall be made in the course of the present description. This however does not limit the possibility of employing the subject device also on sewing machines with plane base or of other kinds.
As is well known, machines with cylindrical bases are particular types of sewing machines, mainly used to perform for instance the assembly of cuffs or to finish hems of shirts or trouser legs or, more in general, to perform stitching on articles of tubular shape. To this end, machines of this type are conceived in such a way that the base whereon the article undergoing the work process advances presents dimensions that are as smell as possible, in order to allow working also on tubular articles of small diameter previously fitted around the base itself.
The reduction in the size of the cylindrical base is, however, limited by the need to provide, in the base itself, for sufficient space to house the various organs of the sewing machine.
In this respect, particular importance is taken on by the need to house in the base of the machine the device for controlling the motion of the transport claws, which are assigned the task of making the article advance correctly in the sewing area.
To this end, the claws are supported and actuated by a control device which transmits thereto a cyclical motion according to an essentially elliptical trajectory, in synchrony with the motion of the other organs of the sewing machine.
Currently, devices of this type normally provide for the transport claws to be fastened to respective plate-shaped oscillating supports, mutually paired according to vertical planes and fitted each with two fork-shaped portions oriented from respectively opposite parts.
To the oscillating supports and, hence, to the claws, a vertical oscillatory motion is imparted by means of a pair of eccentrics mounted on respective rotating shafts and operatively engaged in respective lifting blocks each of which is engaged in one of the fork-shaped portions of both oscillating supports, with the possibility of sliding longitudinally.
To the individual oscillating supports is also transmitted a horizontal oscillatory motion in the direction of advance of the cloth, through respective connecting rods mounted on oscillating shafts, driven independently of each other with angular oscillatory motion each around its own axis.
The synchronous combination of the vertical and horizontal oscillations imparted to the claws confers them the aforesaid ellipsoidal cyclic motion, in such a manner that the claws themselves, at each stitch-forming cycle, emerge from the needle plate to drive the article with a longitudinal translation of predetermined amplitude.
The devices described above present considerable efficiency and operating reliability, so much so that their use is widespread in different types of sewing machines.
However, with particular reference to sewing machines with cylindrical base, it should be noted that the size of the control device for the transport claws is a highly critical factor for the purposes of the dimensional containment of the base of the machine itself. When, as occurs in normal cases, a transport device similar to the one normally used on other types of machines, such as plane-base machines, is employed on the cylindrical base machine, it is practically impossible to reduce the dimensions of the cylindrical base below perimeter development values on the order of 250 mm.
Some manufacturers have been able to reduce the size of the claw control device by effecting a sort of "miniaturization" of the components. In these cases, the size of the cylindrical base has been contained to a perimeter development on the order of 180 mm. However, the reduction in the size of the components also entails a reduction in mechanical resilience and in operating reliability, even employing highly sophisticated, and hence highly expensive, materials and work procedures.
It should also be noted that even the cylindrical bases with a development reduced to values on the order of 180 mm do not fully meet the requirements of the market, wherein the ability to work tubular articles of small size on machines with cylindrical base is in ever increasing demand.